1. Field of the Invention
The subject invention relates to a twist beam for an automotive vehicle, and a suspension assembly including the twist beam.
2. Related Art
Automotive vehicles include a rear suspension assembly connecting the rear wheels together. The suspension assembly includes a pair of longitudinally control arms and trailing arms interconnected by a twist beam, also referred to as a torsion beam. Twist beams of rear suspension assemblies typically comprise a cross-section having an O-shape, C-shape, U-shape, or V-shape, which can be either open or closed. The twist beam should also be rigid enough to prevent bending yet flexible enough to allow torsion. Accordingly, the twist beam is not only a structural member, but also acts as a torsion spring. Example twist beams are disclosed in U.S. Patent Application Publication Nos. 2010/0301577, 2008/0191443, and 2012/0211961.
Twist beams experience a significant amount of stress during use in the automotive vehicle, due to twisting and other factors. Therefore, maximum stress levels, especially those due to twisting, require a minimum material thickness and thus dictate the weight of the twist beam. However, the weight of the twist beam is preferably kept as low as possible since it contributes to the total weight of the automotive vehicle.
The twist beam also controls a roll rate or roll stiffness of the vehicle, which affects the ride and handling of the vehicle. The twist beam provides the roll stiffness by twisting as the trailing arms move vertically relative to one another. The roll stiffness is analogous to a vehicle's ride rate, but for actions that include lateral accelerations, causing a vehicle's sprung mass to roll. Roll stiffness is expressed as torque per degree of roll of the vehicle sprung mass, and is typically measured in Nm/degree. The roll stiffness of a vehicle does not change the total amount of weight transfer on the vehicle, but shifts the speed at which weight is transferred and percentage of weight transferred from a particular axle to another axle through the vehicle chassis. Generally, the higher the roll stiffness on an axle of a vehicle, the faster and higher percentage the weight transfer on that axle. A slower weight transfer reduces the likelihood of vehicle rollover conditions.
The dimensions and design of the twist beam have a significant influence on the roll stiffness. Increasing the thickness of the twist beam can increase the roll stiffness, but this also increases the weight and manufacturing costs. Stabilizer bars are often times used to achieve the desired roll stiffness, especially in twist beams having an open U-shaped or V-shaped cross-section. A closed V-shaped cross-section can also provide adequate roll stiffness. However, twist beams including the stabilizer bar or closed cross-section are costly because they require a complex, controlled, and consistent manufacturing process.